Note on Mixed-Layer Entrainment Closure

Howard P. Hanson Cooperative Institute for, Marine and Atmospheric Studies, 4600 Rickenbacker Causeway, Miami, FL 33149

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Abstract

The entrainment closure for the turbulence energy budgetcommonly used in unsaturated mixed layer models is re-derivedfrom the perspective of potential energy changes, and it isconcluded that the correct physical interpretation of theenergetics based on experimental evidence is that the turbulenceform entrainment at about the 20% efficiency level(not the 4% level). In the case of a cloud-toppedmixed layer, this physical interpretation leads to are-examination of the condition for stratocumulus cloud-topentrainment instability and the conclusion that recentcorrections for liquid water loading may yet be toorestrictive.

Abstract

The entrainment closure for the turbulence energy budgetcommonly used in unsaturated mixed layer models is re-derivedfrom the perspective of potential energy changes, and it isconcluded that the correct physical interpretation of theenergetics based on experimental evidence is that the turbulenceform entrainment at about the 20% efficiency level(not the 4% level). In the case of a cloud-toppedmixed layer, this physical interpretation leads to are-examination of the condition for stratocumulus cloud-topentrainment instability and the conclusion that recentcorrections for liquid water loading may yet be toorestrictive.

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